Various embodiments of injection devices for injecting fuel into a combustion chamber of an internal combustion engine are known from the prior art, in particular in conjunction with storage-type injection systems, such as for example common rail systems for injecting diesel fuel into a combustion chamber of an engine. Such injection devices comprise a nozzle needle guided in a nozzle body, with a seal fit being created at one tip of the nozzle needle between the nozzle needle and the nozzle body. Below the seal fit in the exit direction a number of injection holes are generally arranged, which branch off from a bore on the nozzle body and through which the fuel is injected into the combustion chamber. What are known as micro-bore nozzles are also known here, with which the area below the seal fit, from which the injection holes branch, is as small as possible.
In the case of a small needle lift, for example for a preliminary or subsequent injection, with a micro-bore nozzle poor uniform distribution of fuel or a poor jet pattern may result from the small flow cross-section between the needle and the nozzle body. This results in deterioration of combustion processes in the combustion chamber and therefore to poor levels of exhaust gas emissions from the engine. With the known micro-bore nozzles the configuration of the bore is therefore such that a cross-section before the bore has to be kept large enough, which however also results in a larger micro-bore cross-section. Such conditions mean that improvements in exhaust gas emissions are severely restricted by the relatively large volume of the micro-bore.